1. Field of the Invention
The present invention relates to an endoscope apparatus.
2. Description of the Related Art
Usually, a white light source is used in endoscope apparatus. However, in recent years, endoscope apparatus that enable special light observation such as narrow-band light observation in which a fine structure of a surface layer of mucosa tissue is emphasized with illumination by light in a particular narrow wavelength band (narrow-band light) and fluorescence observation in which fluorescence emitted from a fluorescent substance given in advance or living body tissue have come to be used (refer to JP-B-3,583,731, for example). By virtue of special light observation, endoscope apparatus of this kind can easily visualize living body information that cannot be obtained from an ordinary observation image. For example, they can emphasize a lesion and a fine structure of new blood vessels formed in a mucosa layer or a mucosa lower layer.
In diagnoses using an endoscope apparatus, to find a lesion, it is effective to examine a distant-view image covering a wide range that is taken by wide-angle shooting. And to observe the thus-found lesion, it is effective to examine a short-range-view image taken by enlarged shooting. White light is mainly used for the distant-view observation and narrow-band special light is used for the short-range-view observation to emphasize a fine structure or a lesion. The light source type used is switched in synchronism with an observation magnification change which is caused by a zoom magnification varying manipulation (refer to JP-A-2007-20728, for example).
However, where switching is merely made between white light and special light depending on whether short-range-view shooting or distant-view shooting is being performed, the manner of image display is not varied continuously in link with a zoom magnification varying manipulation. Instead, the illumination light is switched from white light to special light at a particular observation magnification value and the content of the observation image is changed suddenly, which is uncomfortable to the operator. Furthermore, the illumination light cannot be adjusted finely to attain optimum illumination according to the observation magnification.